A typical form for a rotary vacuum pump, already known, is shown in FIG. 1. It comprises a body inside which the rotor rotates eccentrically, which holds the running blades and performs the actual pumping; the aforesaid assembly 1, taken as a whole, is also called the "working block". It is generally connected by screws 3 to a stand 2 which also supports the actuating motor 4. A flexible coupling 5 enables the motion to be transmitted to the rotor of the pump. Lubrication is carried out by causing the oil contained in the rigid casing (housing) 6 to penetrate inside the block 1, said block 1 being immersed inside the housing. The oil which enters the block 1 is then expelled, together with the pumped gas, from the delivery valves and mixes again continually with the oil of the housing 6. For the sake of leak-tightness mechanical play between moving parts (rotor and blades) and fixed parts (body or stator) is very small and precise; the lubricating oil serves to complete the seal by forming liquid films which seal the aforesaid parts moment by moment. So it will be appreciated how the vacuum seal (and hence the efficiency of the pump) can be harmed both by a fall in the properties of the oil and by any dust that may be present, which will be more or less abrasive and obstructive in the internal oil ducts. Rotary pumps are generally powered by an electric motor 4 positioned on their axles. The pump-motor complex is mounted on a base which may be of various kinds, such as 7.
The rotary pump complete with motor is often part of a pump station--stationary or mobile which is erected upon and partially closed by a trestle or frame or bench or cabinet. In such a station the rotary pump, being an element that is in motion and relatively heavy, generally occupies the lower part; the fact that the pump is in this position, and the "compactness" of the station make for complex operations to remove said pump, when it is necessary to perform the inevitable maintenance operations upon it. The frequency of this maintenance depends essentially on the conditions of use, in particular on the working pressure and the nature of the gases that are being pumped. Many applications do in fact exist which demand very frequent maintenance because of the suction of polluting and corrosive gases, sometimes also drawing in abrasive dusts. Correct use of the pump therefore requires operations which range from simply filling up with oil through a total change of the oil load, cleaning the internal parts and replacing worn moving parts, to completely overhauling and possibly changing the entire working block, in appropriate maintenance departments.
As already said, the rotary pump is part of a pump station, which in turn is part of the productive plant. The plant generally consists of a machine characterized by high technology, high cost, and rapid obsolescence; the plant therefore has to be used to its maximum potential to ensure its favorable depreciation. In such a plant the rotary pump is a secondary element as regards value but it is essential for the work, so the frequent shutdown times due to the pump must be absolutely as short as possible.
The solution to this problem that is normally adopted is to keep a reserve pump ready; but this solution is clearly quite burdensome and technically not particularly satisfactory. In fact the need to disconnect the pump from the intake and delivery pipes and the electrical supply etc., and the difficulty of access already referred to, make substitution of the whole pump a very laborious operation and one which in any case requires it to be checked that the connection of the vacuum line has been correctly performed. Sometimes the remedy adopted is the radical one of keeping an entire station ready, with a further heavy increase in fixed assets. To do this however does not eliminate the loss of time needed to prepare the connections, while the operations necessary for maintenance simply become parallel to production time.
It is apparent from the aforegoing that until now no solutions have been devised which solve the problem of performing the operations of maintenance and restoring the pump to working order with a minimum of lost time and with contained costs.
In solutions such as that shown in FIG. 1, it is possible to replace the entire working block in a single operation. To do this it is also necessary to empty the oil and disassemble the housing 6 in order to gain access to the working block and extract it after unscrewing the screws 3 which connect it to the stand. Such an operation will inevitably involve polluting the working environment through the dripping of oil deposited on the walls of the working block. This is prejudicial to the good quality of the process when a high degree of cleanness is required in the environment, and it is intolerable for worker safety when the oil is contaminated with corrosive or toxic substances. The replacement of the working block therefore requires the whole pump to be in some way transported into a fitted workshop.
In one known solution of a pump with a particular internal arrangement it is possible to extract and replace the working block by gaining access through an opening in the top of the housing of the pump. But this case again does not solve the problem of avoiding direct contact between the operator and the contaminated oil, and dispersion of the oil in the working environment. In installations which limit access to the pump, the opening of the housing and the replacing of the working block can still prove to be extremely laborious. Since the work has to be done by hand only, this principle only allows maintenance on pumps of limited weight and hence limited capacity.